The present invention generally relates to the art of paper handling and, in particular, to a method and a device for controlling the orientation and alignment of individual sheets of paper passing on a conveyor.
Sheets of paper that travel individually along a conveyor are usually required to have a predetermined alignment and orientation. Conventionally, the conveyor has an alignment rail that extends parallel to the direction of sheet travel and the sheets are driven on the conveyor with a major component in the general travel direction and a small component towards the alignment rail, thereby forcing the sheets to move into abutment with the rail. An alignment rail may also correct potential orientation errors of the sheets by slightly rotating the sheets in the course of the alignment process. With increasing speeds of sheet travel and with relatively light paper, however, there is a risk that the sheets are damaged by being forced into abutment on the alignment rail. Also, such an alignment rail can only correct for relatively small errors of sheet alignment and orientation, and it can neither introduce a major offset of sheet travel with respect to an original sheet alignment, nor can it produce a 90xc2x0 rotation of the sheets so as to change their orientation or direction of travel, in a wide range of paper weight and at high speeds of sheet travel.
The present invention provides a method and a device for controlling the orientation and alignment of individual sheets of paper passing on a conveyor, wherein even large errors of sheet alignment and sheet orientation can be corrected reliably and without the risk of sheet damage in a wide range of paper weight and at high continuous speeds of sheet travel, and wherein optionally an offset of sheet travel with respect to an original sheet alignment can be introduced, or a 90xc2x0 rotation of the sheets can be produced so as to change the orientation or direction of travel of the sheets.
In accordance with the invention, a method of controlling at least one of the orientation and alignment of individual sheets of paper travelling on a conveyor is provided. Each sheet passes over a pair of closely spaced rotating disks and the sheet is locally engaged with each disk in a limited contact area, and the contact areas between the sheet and each disk are varied so as to achieve a target orientation or alignment of the sheet. When a sheet is first engaged by a rotating disk, the point of contact should be such that, at the point of contact, the tangential speed component of the disk is parallel to the sheet travel direction on the conveyor section upstream from the disks. Also, the tangential speed component should be of the same value as the upstream travelling speed of the sheet. As soon as the sheet is released from the upstream conveyor section, it is fully under control of the rotating disks, and the sheet travel direction can be acted on by changing the points of engagement between the sheet and the disks to shift the sheet laterally, or the disks are driven at different speeds as a sheet passes to rotate the sheet. Both actions can be combined to change the travel direction and simultaneously to rotate the sheet, whereby both of the alignment and the orientation of the sheet are controlled. As soon as the sheet is engaged by the downstream conveyor section, it should be released from the rotating disks. Just prior to this moment of sheet transfer from the pair of rotating disks to the downstream conveyor section, the sheet should be engaged by the disks at locations where the tangential speed component has the same direction as the travel direction of the downstream conveyor section. The travel directions of the upstream and downstream conveyor sections can be the same or different from each other and even be perpendicular to each other, the proposed method being capable of producing a full 90xc2x0 rotation of a sheet without having to slow-down the sheet travel speed upon passing over the rotating disks.
The present invention also provides a device for controlling at least one of the orientation and alignment of individual sheets of paper travelling on a conveyor, which is particularly designed to perform the inventive method. The device comprises a pair of closely spaced rotating disks arranged on a sheet travel path between upstream and downstream sections of the conveyor. The device also comprises a pair of engagement members each associated with one of the disks to define a sheet passage gap where the sheet is locally clamped. The engagement members are each movable opposite a respective disk within a 90xc2x0 sector of the disk defined between a radius parallel to and a radius perpendicular to the sheet travel direction. The engagement members are positioned in synchronism so that the sheet passing over the continuously rotating disks is driven by each sheet in the same direction, but the speed of rotation of the disks may be varied between the disks as the sheet passes so as to produce a rotation of the sheet.
To reduce the time necessary for movement of the engagement members, a plurality of selectively activatable engagement members can be arranged at regular intervals about the periphery of each disk, and only one of these engagement members will be active at a given time.
An engagement member can be an idle roller mounted on a first end of a pivotal carrier arm the pivot axis of which is co-axial with the axis of rotation of the associated disk. If a plurality of idle rollers are provided for each rotating disk, they are mounted on a carrier disk arranged opposite a respective rotating disk, the carrier disk being co-axial with the rotating disk and the idle rollers being retractable.
In an alternative embodiment, the engagement members are materialized by pneumatic means. Specifically, each rotating disk has a plurality of perforations distributed over its periphery, and a suction member is arranged on a side of the disk opposite a sheet facing side of the disk, the suction member being aligned with the perforations and movable about the axis of rotation of the disk within a 90xc2x0 sector of the disk.